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EARTH Phần 10

MINING For thousands of years, people have mined native metals such as gold, silver, and copper, and turned them into tools, weapons, and ornaments. At some point, they discovered that heating far more abundant metal ores in a charcoal furnace separated the pure metal, and this led to the widespread use of materials like iron. Other minerals such as flint, building stone, and gemstones have also been mined since prehistory. Fuels such as coal, oil, and natural gas have been exploited more recently. The three main techniques are quarrying, deep shaft mining, and drilling into the ground to tap buried oil. | MINING oSTONE QUARRY Building stone has always been a valuable resource. Originally chipped 9 PANNING FOR GOLD The fact that gold exists naturally in its native form makes it possible for For thousands of years people have mined native metals such as gold silver and copper and turned them into tools weapons and ornaments. At some point they discovered that heating far more abundant metal ores in a charcoal furnace separated the pure metal and this led to the widespread use of materials like iron. Other minerals such as flint building stone and gemstones have also been mined since prehistory. Fuels such as coal oil and natural gas have been exploited more recently. The three main techniques are quarrying deep shaft mining and drilling into the ground to tap buried oil and gas reserves. out and shaped using hand tools it is now extracted using carefully placed explosive charges or sliced out by machines. The stone being quarried here in Italy is Cararra marble one of the finest of all stones. It has been used since Roman times for prestige building projects and sculptures such as the work of Michaelangelo. people to extract it using the most basic methods such as panning. This involves swirling water through gold-bearing sediments to carry away the lighter particles and leave the heavy gold. Gold is so rare however that days of work by these panners in Vietnam are likely to yield just a few grains of the precious metal. STRIP MINE Where minerals occur near the surface they can be extracted by digging out a deep pit or strip mine. The Bingham Canyon mine in Utah has been under excavation since 1908 and is now the largest artificial hole on Earth. The pit itself is miles 1.2 km deep and measures 2 miles 4 km across. 0 HYDRAULIC MINING Heavy metals such as gold can be extracted from soft sediments using high-pressure hoses. The principle is similar to panning but it processes far more material. The sediments are washed through enormous sluices that retain the metal .